1. Field of the Invention
This invention relates generally to a method for detecting and correcting the amount of an skew of image, and more particularly to a method and an apparatus for detecting and correcting the amount of skew of an image in which the method and apparatus are suitable when used in an image filing system equipped with an automatic paper feeding device.
2. Description of the Related Art
Image filing systems have recently come on the scene as the fourth office automation machine next to a word processor, a personal computer and a facsimile, attracting the public's attention as a means for pushing forward the concept of paperless document filing in offices, laboratories, etc. This image filing system is adopted to store a large volume of image data in an optical disk, from which image data can be read quickly as needed for printing. As a consequence, use of image filing systems have deeply spread particularly into departments where large volumes of documents are produced and, as a result of which, labor power for inputting such documents should be minimized.
Regarding this image inputting work, in a conventional image filing system equipped with an automatic paper supply device to automatically supply the documents to be inputted, the need to avoid a skew (tilt) which might occur between a document and a scanner, whereby the images would be inputted in a skewed posture, is inevitable. Yet, although such skew could be reduced to a very small amount, character rows in a document were often initially skewed.
A solution to these conventional problems has hitherto been proposed by Japanese Patent Laid-Open Publication (KOKAI) No. 14277/1987. The system of this prior art performs contour extracting from a document image, obtains a skew from the extracted characters and ruled lines, and then achieves the automatic correcting of the skew. Specifically, a specific amount of data is obtained with respect to the contour extracted from the image, and this specific amount of data is integrated in various directions. Then, a direction in which the integration value will be the peak is obtained, and the entire image is turned by an angle which is made by the direction with respect to the edge of paper sheet. By thus obtaining a skew of the entire document image from the contour, it is possible to automatically correct the image data in which a skew is created.
As mentioned above, the prior system obtains the amount of skew from the extracted contour data and corrects the skew of input an inputted image by using the amount of skew. Therefore, it is unnecessary to check by eye, which was necessary even with a scanner with an automatic supply device, so that the rate of registering the image data can be improved.
However, with this prior system, because the angle of skew was simply obtained and the entire document image was corrected by merely using the obtained angle of skew, problems with respect to processing time were still prevalent.
Specifically, when measuring an angle of skew, it was necessary to integrate a characteristic amount of data in all directions covering the range in which the skew of input image existed. Reportedly, since this integral included many integrating and summing operations, it resulted in a huge amount of calculation which would take several tens of seconds even by using a general large-sized computer whose processing rate is about 20 MIPS. Practically, this disadvantage is revealed particularly in an image filing system, which is a small-sized office automation machine.
Further since, when correcting the skew of an image, the image was turned by merely using the obtained angle of skew, such a very small amount of skew angle that could not be sensed by a human being would be unnecessarily corrected.